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From: anita@sun.udel.edu (Anita Marie Hoover)
Newsgroups: comp.text.tex
Subject: LaTeX \\
Keywords: \\
Message-ID: <13379@sun.udel.edu>
Date: 14 Aug 90 20:33:44 GMT
Organization: University of Delaware
Lines: 43

The strangest problem surfaced yesterday.  Here is a simple
array that someone showed me and asked why it wasn't working. Here
is the example.

    \[
    \begin{array}{ccc}
    [A_{1} & [B_{2}] & \\
    [D_{2}] & [B_{2}] & [C_{2}]
    \end{array}
    \]

would get the following error

    ! Missing number, treated as zero.
    <to be read again>
                       D
    <argument> D
                _{2}
    \@argarraycr [#1]->\ifnum 0=`{\fi }${}\ifdim #1
                                                   >\z@ \@xargarraycr
    {#1}\else ...
    l.6 [D_{2}]
                & [B_{2}] & [C_{2}]
    ?


Well after looking at this for too long -- I realized that the
problem was that the \\ on the previous line was trying to use
the [D_{2}] as an optional argument for \\.  Of course it would
cause an error, but should LaTeX really give an error?  Anyway
if you do the following the problem is solved

    \[
    \begin{array}{ccc}
    [A_{1} & [B_{2}] & \\
    ~[D_{2}] & [B_{2}] & [C_{2}]
    \end{array}
    \]

Any comments?

Anita Hoover
University of Delaware